docs: def parse_vlan_range_mappings(mappings):
      """Parse vlan range mappings.
  
      Mappings must be a space-delimited list of provider:start:end mappings.
  
      The start:end range is optional and may be omitted.
  
      Returns dict of the form {provider: (start, end)}.
      """
      _mappings = parse_mappings(mappings)
      if not _mappings:
          return {}
  
      mappings = {}
      for p, r in six.iteritems(_mappings):
          mappings[p] = tuple(r.split(':'))
  
      return mappings